1. Field of the Invention
The present invention relates to apparatus for generating electric power, and, more particularly, but not by way of limitation, to generating apparatus incorporating an automobile alternator as the power source.
2 Description of the Prior Art
In many parts of the world electric power is not readily available so that persons working in such areas must often take electric power generating apparatus to a job site in order to efficiently carry out such simple tasks as drilling a hole in a piece of metal or welding two pieces of metal together. Such generating apparatus will often be called upon to operate a variety of tools, each having its own power requirements which may, or may not, coincide with the requirements of other tools used at the site. Because of this variety, it is desirable that the generating apparatus be provided with a simple mechanism for adjusting the electrical characteristics of the power generated thereby to match the needs of the various tools at the job site.
It is also desirable that the generating apparatus incorporate parts which are interchangeable with other equipment likely to be found at a remote job site so that, if necessary, the generating apparatus may be maintained in operation by using repair parts provided for such other equipment. Skilled labor is often available at such sites only at a premium so that overseas supply of repair parts is to be avoided where possible. A piece of other equipment which usually accompanies workers to remote areas is a vehicle such as a truck or automobile.
It is known that the alternator found in the electrical system of a vehicle is capable of generating a voltage of sufficient amplitude to operate hand held power tools and that such an alternator is capable of providing power suitable for welding. For example, U.S. Pat. Nos. 3,761,727 and 3,845,321, issued to Santilli on Sept. 25, 1973 and Oct. 29, 1974 respectively, illustrate the use of a motor vehicle electrical system as a source of power for electrically driven hand tools. Such a capability is built into the alternator to permit the alternator to charge the vehicle battery at low speed operation of the vehicle engine which drives the alternator. As is well known, the electromotive force generated in an alternator or generator winding depends both upon the strength of a magnetic field relative to which the winding is rotated, either by rotating the winding or the source of the magnetic field, and to the rate of rotation. Thus, if the alternator is to be capable of generating a voltage sufficient to charge the vehicle battery when driven at a low speed, it will be capable of generating a higher voltage when driven at a higher speed. Such higher voltages are not desirable if the alternator is to be used for no purpose other than charging the battery and are prevented from occurring by using an electric current, referred to herein as a field current, to establish the magnetic field relative to which the winding or windings connected to the alternator output are rotated. The field current is supplied by the vehicle battery via a voltage regulator which varies the field current as the engine speed is increased or decreased to offset changes in the speed at which the alternator is driven with opposing changes in the magnetic field.